1. Field of the Invention
The present invention generally relates to sensing devices employing floatation means for supporting a sensing element near the surface of a liquid and, in particular, to such devices as used for detecting hydrocarbon substances on the surface of ground water.
2. Statement of the Prior Art
Wide spread use of fossil fuels in today's world has caused many problems with the pollution of ground water and drinking water supplies by leakage of such fuels and various hydrocarbon containing substances into the ground water. To help detect this problem, sensors have been developed for detecting the presence of such substances on the surface of ground water. One such sensing device is described in U.S. Pat. No. 4,221,125 which employs a semiconductor diode positioned in proximity to the surface of a body of water by a float means for detecting the presence of hydrocarbon substances. A related device is described in U.S. Pat. No. 4,223,552. It has been found, however, that additional information is also desirable such as knowing the amount of hydrocarbons present on the surface of ground water and either the rate of increase or decrease of the hydrocarbon substances present. Problems, however, have been encountered in the reliability of long term sensing devices due to the corrosion of the floatation means caused by various chemical substances present in the ground water and the subsequent dislocation of the sensing element supported thereby in respect to the water's surface.